Liven Up Your Fish Pot Pie With Shrimps and Mushrooms

Ingredients

• 550 g potatoes (peeled and cut into chunks)
• 5 tbsp Greek-style yogurt
• 1 tbsp reduced-salt margarine
• 1 small onion (sliced)
• 400 g white fish fillets
• 2 cups low-fat milk
• 2 bay leaves
• 4 sprigs parsley
• 80 g small pasta shells
• 4 tbsp cornstarch
• 1/2 tsp mustard powder
• nutmeg (freshly grated, to taste)
• 120 g cooked peeled shrimp
• 80 g mushrooms (thinly sliced)
• 4 tbsp parsley (chopped)
• pepper (to taste)